1. Field of the Invention
The present invention relates to an imaging apparatus, an imaging method and an imaging system.
2. Description of Related Art
Autofocus is a function of automating focusing of a camera.
The autofocus is performed by control action including two main steps.
First, at step 1, a focusing degree in a focusing area is measured for determination of focusing.
Then, at step 2, a search for a focusing position where the focusing degree becomes maximum is made using the focusing degree measured at step 1. In related art, the hill-climbing search has been often used. As the search method, a method of determining a lens position area with the focusing degree at a predetermined threshold level or higher and moving the lens from the range in a direction in which the gradient of the value of the focusing degree increases has been employed. Further, a fine search is made around the peak for searching for the lens position at the peak.
As a background art of the technology field, JP-A-2009-42621 (Patent Document 1) has disclosed “Imaging means for converting a subject image into an electric signal, and a focus adjustment mechanism that adjusts a focus position of a lens based on an evaluation value calculated from the signal output from the imaging means and representing sharpness of an image are provided. Focus area setting means for setting a focus area as an evaluation value calculation area on an imaging screen, a lens moving means for moving the lens within a range of focus adjustment, and evaluation value calculating means for calculating an evaluation value with respect to each lens position moved by the lens moving means are provided, and an evaluation value acquisition operation for acquiring an evaluation value in each lens position while moving the lens is started from a near side and imaging is performed in the lens position with the evaluation value equal to or more than a predetermined threshold value.”
In the autofocus control disclosed in Patent Document 1, there is the following problem.
First, in an imaging environment with a low contrast value such as the case of low illuminance, the value of the focusing degree is susceptible to noise and the true peak position may be erroneously recognized due to noise. Accordingly, it is impossible to control the lens position to an appropriate focusing position and a subject is out of focus.